Post purge system for gas burners

ABSTRACT

A post purge device for a fuel burning apparatus wherein a fuel pressure sensing means is disposed between and in communication with a main fuel line supplying fuel to a fuel burning apparatus and a diaphragm, the fuel pressure sensing means containing a fluid therein wherein movement of the fluid is determined by the pressure in the fuel line thereby causing movement of the diaphragm in response to the movement of the fluid, the diaphragm being in electrical communication with a combustion air blower wherein a predetermined amount of movement of the diaphragm controls the energization of the combustion air blower.

United States Patent 11 1 Mutchler 1 1 POST PURGE SYSTEM FOR GAS BURNERS[75] Inventor: Paul A. Mutchler, University City,

[73] Assignee: American Air Filter Company, 1nc.,

Louisville, Ky.

22 Filed: Dec. 20, 1972 211 Appl. No.: 316,763

[111 3,801,258 [451 Apr. 2 1974 3,388,862 6/1968 Gabrielson 431/12 XPrimary Examiner-Edward G. Favors [57] ABSTRACT A post purge device fora fuel burning apparatus wherein a fuel pressure sensing means isdisposed between and in communication with a main fuel line supplyingfuel to a fuel burning apparatus and a diaphragm, the fuel pressuresensing means containing a fluid therein wherein movement of the fluidis determined by the pressure in the fuel line thereby causing movementof the diaphragm in response to the movement of the fluid, the diaphragmbeing in electrical communication with a combustion air blower wherein apredetermined amount of movement of the diaphragm controls theenergization of the combustion air blower.

4 Claims, 2 Drawing Figures [52] U.S. Cl. 431/90 [51] Int. Cl F23n l/02[58] Field of Search... 431/90, 12; 137/100, 101.21

[56] References Cited UNITED STATES PATENTS 2,986,207 5/1961 Scogin431/90 3,393,965 7/1968 Vaughan.. 431/12 3,522,661 8/1970 Scott r v r431/2 X 2,976,689 3/1961 Dodds et a1; 137/100 X POST PURGE SYSTEM FORGAS BURNERS BACKGROUND OF THE INVENTION This invention relates to a postpurge system for a gas burner. More particularly, the invention relatesto a post purge system for gas burners utilizing a fuel pressure sensingmeans in combination with a diaphragm, the diaphragm being responsive tothe fuel pressure sensing means and in turn being the means formaintaining the actuation of an electrical circuit including acombustion air blower for a burning apparatus after the main fuel gas tothe burning apparatus has been closed off.

In the purging of a fuel burning apparatus after the fuel gas has beenshut off, many elaborate devices have been provided for operating theapparatus combustion air blower for a preselected period of time asmeans for purging unburned gas from the apparatus thereby providingavery desirable feature for any gas burning apparatus. Electricallyoperated timing devices have found wide acceptance as the means formaintaining the combustion air blower in operation after the main fuelgas has been shut down. These timing devices keep the combustion airblower energized for a preselected period of time after a fuel gassupply valve has been fluid 7 therein, fluid 7 being heavier than thefuel gas,

closed off or a pressure sensing means has indicated a fuel gas linepressure below a preselected pressure setting. Thus, for a preselectedperiod of time, the combustion air blower remains in operation therebypurging the fuel burning apparatus. However, most of the arrangementsutilizing electrical timing devices are quite expensive and elaborate intheir construction.

SUMMARY OF THE INVENTION In the present invention, it is recognized thatit is desirable to provide a post purge system for a gas burningapparatus which is inexpensive, durable, and easily installed.Furthermore, it is recognized that it is desirable to provide a postpurge system which does not require elaborate electrical timing devices.

The present invention advantageously provides a straightforwardarrangement for a post purge system for a fluid fuel burner which isinexpensive, durable and easily constructed. The present inventionfurther provides for the utilization of a fuel pressuresensing meansdisposed between a main gas line and a diaphragm means, the diaphragmmeans being responsive through the pressure sensing means to thepressure in the main gas line, the diaphragm being in electricalcommunication with a combustion air blower to maintain actuation of thecombustion air blower circuit after the main gas fuel line has beenclosed off.

Various other features of the present invention will become obvious tothose skilled in the art upon reading the disclosure as set forthhereinafter.

More particularly, the present invention provides a post purge devicefor a fuel burning apparatus comprising: a main fluid fuel line incommunication with a fluid fuel supply and a fuel burning apparatus; afuel pressure sensing means disposed between the main fuel gas line anda diaphragm means, the fluid pressure sensing means having a first fluidtherein responsive to pressure in the fuel gas line, the diaphragm meansbeing operative in response to movement of the first fluid; and, acombustion air blower in electrical communicative relation with thediaphragm means.

It is to be understood that the description of the examples of thepresent invention given hereinafter are not by way of limitation andvarious modifications within the scope of the present invention willoccur to those skilled in the art upon reading the disclosure as setforth hereinafter.

Referring .to the drawing:

FIG. 1 of the drawing diagrammatically illustrates one preferredapparatus of this invention; and,

FIG. 2 of the drawing diagrammatically illustrates another preferredapparatus of this invention.

The post purge device of the present invention in FIG. 1 includes acombustion air blower l to supply combustion air by means of conduit 2to a fuel gas burner 3. Fuel gas to fuel gas burner 3 is suppliedthrough conduit 4 which has a branch conduit 5 in communication with afuel pressure sensing means illustrated as the U-tube 6.

The U-tube 6 defined by legs 8 and 10, includes a such as, for example,a silicon oil. Leg 8 is in communication with branch conduit 5 andcontains the fuel gas in the top portion and fluid 7 in the lowerportion. The U-tube 6 further includes a restriction at the bend of thetube 6, the restriction being exemplified as a limiting orifice 9.Limiting orifice 9 is provided so that when the fuel gas pressure in thetop of leg 8 is decreasing,

the flow of fluid 7 in the leg 10 is limited in its movement into theleg 8 in equalizing the pressures in the legs '8 and 10. Furtherdescription of the flow limiting orifice 9 will be discussedhereinafter.

Leg 10 of the U-tube 6 extends upwardly and communicates with a housing11 which includes a diaphragm 12 therein. In the space between the topof the fluid 7 and the diaphragm 12 is a fluid l3, fluid 13 beinglighter than the fluid 7 in theU-tube 6 and exemplified in the presentexample as air. The fluid 13 disposed between the fluid 7 and thediaphragm 12 maintains a pressure on the diaphragm 12, the amount ofpressure on diaphragm 12 depending upon the level of the fluid 7 in leg10. Housing 11 further includes an electrical contact switch 14 which isnormally open but operable by the movement of a vertically extending rod25 in response to movement of diaphragm 12. For example, when thediaphragm 12 moves upward, rod 25 urges normally open switch 14 closedand when diaphragm 12 moves downward in response to a decrease of thefluid 13 pressure in U-tube leg 10, rod 25 urges contact switch 14 to anopen position. The lines com pleting the circuit between normally openswitch 14 for blower 1 and the main power source are line 16 which isconnected to the main switch 17 of the main power source and the line 15disposed between switch 14 and blower 1. Line 18 is an electrical lineconnecting the combustion air blower l to a circuit within electricalbox 24 which, through a plurality of connections (not shown),communicates with the line 19 leading from the box to the main powerswitch 17, thus completing a circuit including the normally open switch14, switch 14 being actuated in response to the main fuel gas pressurethrough the aforementioned U-tube 6. The portion of theelectricalcircuit disposed between lines 18 and 19 may include, for example,safety control devices which open the circuit upon detection of anunsafe condition thereby de-actuating the combustion air blower l.

In the main gas line 4 is a solenoid operated valve 21, a pressureregulator 22, and a main gas supply valve 23. The solenoid operatedvalve 21 is of any suitable commercial construction. The operation ofthe solenoid valve 21 is by an electrical circuit (not shown) which isadapted to maintain the valve 21 in an open position during theoperation of the gas burner 3. Pressure regulator 22 is included in themain fuel gas conduit line 4 to maintain a preselected pressure on themain gas line whenever the gas burner 3 is in operation. The main gassupply valve 23 is provided to manually control the gas to the gasburner 3.

, Under'normal operations of a burning apparatus, the combustion airblower 1 is energized and supplies combustion air to the burner 3 by wayof conduit 2. Fuel gas flow to the burner 3 is maintained through fuelgas conduit 4 with fuel gas under line pressure being in contact withfluid 7 in leg 8. Pressure of the fuel gas on fluid 7 in leg 8 forcesthe fluid 7 into leg 10 thereby compressing the fluid 13 in leg 10.Diaphragm 12 being operable in relation to the pressure exerted by fluid13 is maintained in an upwards position due to the pressure exerted byfluid 13 thereby maintaining switch 14 in a closed position through rod25. Thus, as long as the fuel gas pressure in conduit 4 exceeds apredetermined fuel gas pressure setting, blower 1 will remain energized.

On the shut down and purging of the gas burner 3, the switch whichenergized the solenoid operated valve 21 is opened thereby closing valve21. The volume of fuel gas in conduit 4 then decreases causing the fuelgas pressure in the top portion of leg 8 to decrease, the result beingthe fluid 7 in leg 10 moving into leg 8 replacing the void left by thefuel gas. Thus, the pressure on diaphragm 12 decreases in response tomovement of fluid 7. However, the flow limiting orifice 9 restricts theflowof the fluid '7 from leg 10 into leg 8 thereby decreasing thepressure on diaphragm 12 at a rate slower than the decreasing pressurein conduit 4. At a preselected pressure on the diaphragm 12, thediaphragm 12 in combination with rod 25 will move downward a sufficientdistance so that at a preselected point, switch 14 opens. Flow limitingorifice 9 having a predetermined opening therein will, determine thepost purge time of the blower based upon the decreasing volume in leg 10simultaneously decreasing pressure on diaphragm 12. If the opening inthe orifice 9 is relatively small in comparison with the inside diameterof the U-tube 6, the time for the fluid in leg 10 to move through theorifice 9 and into leg 8 will require a much longer time than if theorifice 9 is relatively large.

FIG. 2 illustrates another preferred embodiment of the present inventionincluding means for maintaining energization of the blower 1 undercertain conditions even though switch 14 is open or the blower isdisconnected from the circuit including the pressure switch 14. In thisexample, a second circuit is connected to blower l in parallel with thecircuit including line 16 and switch 14. This circuit includes linedisposed between switch 17 and blower 1. Line 30 is provided with amanual on-off switch 31 and a normally open contact switch 32, normallyopen contact switch 32 being operable to a closed position in responseto actuation of relay 33. Also provided is a line 34 disposed betweenswitch 14 and blower 1. Line 34 includes a normally closed contactswitch 35, normally closed contact switch 35 being operable to an openposition in response to actuation of relay 33.

Relay 33 is energized in response to changes in preselected operatingconditions. For example, in electronic or amplifying type electricalcombustion relays, the power supply to the combustion air blowergenerally provides line current for auxiliary safety devices which inturn powers the programming system of the combustion relay. Without therelay 33 a feed back situation would exist and an unsafe situation wouldresult whereby the apparatus would continue to operate after theoperating switch was satisfied and the burner was to be deactivated.

It will be realized that various changes may be made to the specificembodiment shown and described without departing from the spirit andscope of the present invention.

What is claimed is:

1. A post purge device for a fuel burning apparatus comprising:

a. a main fluid fuel line in communication with a fluid supply and afuel burning apparatus;

b. a fuel pressure sensing means disposed between said main fluid fuelline and a diaphragm means, said fuel pressure sensing means being aU-tube having two legs with a flow limiting device therein, one leg ofsaid U-tube being in communication with said main fuel gas line and thesecond leg of said U-tube being in communication with said diaphragmmeans, said fuel pressure sensing means having afirst fluid thereinresponsive to pressure in said fluid fuel line, said diaphragm meansbeing opv erative in response to movement of said first fluid;

and,

c. a combustion air blower in electrical communicative relation withsaid diaphragm means.

2. The post purge device of claim 1, said first fluid being heavier thansaid fluid fuel, said U-tube having a second fluid in said second leg,said second fluid being lighter than said first fluid and disposedbetween said first fluid and said diaphragm means. i

3. The post purge device of claim 2 wherein said diaphragm meansincludes a rod in communication with a normally open switch, said switchbeing in an electrical circuit which includes said combustion air blowerwhereby upward movement of said rod in response to said second fluidpressure closes said switch and decrease in said second fluid pressurereleases said rod whereby said switch is moved to an open position.

4. The post purge device of claim 1 including means for maintaining saidcombustion air blower energized under preselected conditions independentof said diaphragm means.

1. A post purge device for a fuel burning apparatus comprising: a. amain fluid fuel line in communication with a fluid supply and a fuelburning apparatus; b. a fuel pressure sensing means disposed betweensaid main fluid fuel line and a diaphragm means, said fuel pressuresensing means being a U-tube having two legs with a flow limiting devicetherein, one leg of said U-tube being in communication with said mainfuel gas line and the second leg of said U-tube being in communicationwith said diaphragm means, said fuel pressure sensing means having afirst fluid therein responsive to pressure in said fluid fuel line, saiddiaphragm means being operative in response to movement of said firstfluid; and, c. a combustion air blower in electrical communicativerelation with said diaphragm means.
 2. The post purge device of claim 1,said first fluid being heavier than said fluid fuel, said U-tube havinga second fluid in said second leg, said second fluid being lighter thansaid first fluid and disposed between said first fluid and saiddiaphragm means.
 3. The post purge device of claim 2 wherein saiddiaphragm means includes a rod in communication with a normally openswitch, said switch being in an electrical circuit which includes saidcombustion air blower whereby upward movement of said rod in response tosaid second fluid pressure closes said switch and decrease in saidsecond fluid pressure releases said rod whereby said switch is moved toan open position.
 4. The post purge device of claim 1 including meansfor maintaining said combustion air blower energized under preselectedconditions independent of said diaphragm means.